This invention relates to circuit interrupters and more specifically relates to a novel puffer interrupter having arc energy assist for operating the interrupter contacts during high current arc interruption operation.
Puffer-type interrupters are well known and commonly consist of a cooperating movable and stationary contact, with the movable contact carrying a nozzle which defines an axial gas flow path in the area between the separating contacts when the contacts are opened. The moving contact and the nozzle carried thereby are commonly fixed to a cylinder which moves relative to a fixed piston so that, during the interrupting operation, the volume between the piston and cylinder is compressed and produces a flow of gas through the nozzle and, thus, through the arc drawn between the separating contacts. The gas commonly is an electronegative gas such as sulfur hexafluoride which may be under atmospheric, or some relatively low positive pressure. An operating mechanism of any desired type is connected to the movable contact and nozzle assembly.
In a puffer interrupter, a relatively large energy output is required from the operating mechanism to provide the necessary force to compress and move gas through the arc space. The operating energy needed from the operating mechanism increases also as a function of the current being interrupted for the following reasons:
First, the ability of the puffer breaker to interrupt current is generally related to the differential pressure across the nozzle which is produced by the movement of the relatively movable piston and cylinder within the puffer interrupter. It is necessary, as interrupting current level increases, to increase the diameter of the nozzle in order to control "clogging" of the nozzle. However, increased nozzle diameter implies increased mass flow of gas, so that to develop the desired differential pressure across the nozzle, the compression piston must be enlarged or the operating volume of the compression piston must be increased. In either case, the mechanism energy needed for moving the movable contact assembly must be further increased.
Secondly, as the interrupting current level increases, the arc energy input into the breaker is increased and the pressure and temperature of the gas being compressed is increased proportionally. A further increase in operating mechanism energy is required to overcome the gas pressure force which opposes movement of the nozzle assembly.